A Study of Seismic Anisotropy of Wenchuan Earthquake Sequence

Abstract

AbstractUsing aftershock data of the 2008 Wenchuan earthquake, recorded by seismic stations in the seismic source area and around, with the systematic analysis method (SAM) of shear‐waves splitting, this paper analyzes the anisotropic characteristics in the crust along the Longmenshan fault belt where the Wenchuan earthquake occurred and obtains the directions of the principal compressive stress field in the crust and its spatial distributions. The results show spatial differences: plotting a boundary approximately in Anxian area in the middle of Longmenshan fault belt, the polarization directions of fast shear‐waves at stations located at the northeast segment of Longmenshan fault belt are at NE direction, consistent with the strike of the faults. However, the polarization directions of fast shear‐waves at stations located at the southwest segment are at NW direction, perpendicular to the strike of the faults. This pattern also indicates that the southwest segment of the Longmenshan faults are mainly in thrust fault and the northeast segment are of obviously strike‐slip component. In this study, the polarization directions of fast shear‐waves are scattered at stations near the intersection area of the Longmenshan faults, the Xianshuihe faults and the Anninghe–Xiaojiang faults. It is possibly attributed to the local complex geological tectonics around the seismic source area, consistent with the characteristics of the complex direction of the principal compressive stress in this zone.